An old enemy of Sake and the sake brewer is Hiochi-kin or hiochi bacteria that spoils sake as it grows and reproduces. Unlike most bacteria (bugs for short) hiochi-kin does not mind alcohol and some even like alcohol. So as most Lactobacilli, which are heavy lifters in Kimoto and Yamahai moto styles of sake, will die off as the alcohol levels increase hiochi-kin does not. The other factor that usually keeps the bugs out is low pH levels like those found in sake which are a result of acids created in or added to the moto. However these hiochi-kin also like low pH, highly acidic environments.
As it turns out, hiochi-kin is a lactic acid bug or more specifically it is one of two bugs Lactobacillus (L.) homohiochi and L. fructivorans (a.k.a. L. heterohiochi). These are the “true” or “obligate” hiochi-kin and need hiochic Acid (more commonly known as mevalonic acid) for their growth. Other hiochi-kin or sake spoilage bugs are referred to as “facultative” and include: L. fermentum, L. hilgardii, L. casei, L. paracasei and L. rhamnosus.
Koji produces the needed hiochic acid. The fact that “true” hiochi-kin need hiochic acid implies that these bugs are highly adapted to sake production. Thus they have few other environments in which they can grow. Hiochic acid is an intermediate compound in the biosynthesis of many other compounds so it is not normally seen in a stable state (i.e., not part of a biosynthesis process). The chemical makeup of hiochic acid follows.